Pituitary adenomas and hyperprolactinemia have been recognized in a substantial number of women. The possible relationship to estrogen exposure and oral contraceptive use is a matter of intense current interest. Estrogens are thought to increase prolactin secretion and pituitary growth, at least in part, by a direct pituitary effect. These effects are likely to be mediated by initial attachment to cytoplasmic receptors. The relationship between estrogens and the pituitary will be examined as follows: 1) Study if human pituitary prolactin secreting adenomas contain estrogen receptors and other steroid hormone receptors. 2) Attempt to investigate properties of human prolactin secreting pituitary adenomas in culture. 3) Study pituitary tumorigenesis in response to estrogens in rodents. Contrast the pituitary estrogen receptor system and the chronic estrogen responses in strains that do and do not develop pituitary tumors with chronic estrogen administration. Investigate the effects of an anti-estrogen tamoxifen on tumor development and growth. 4) Investigate the use of a high energy emitting radioactive iodinated estradiol derivative for selective pituitary (and adenoma) imaging in the living animal. These studies may increase our understanding of mechanisms whereby estrogens may be involved in the development and the growth of human prolactin secreting adenomas and provide leads for potential prevention, diagnosis or treatment.